Amplifier



March 31, 1942. H. DUBBERKE 2,277,662

AMPLIFIER l Filed Jan. 4, 1939 HA NS D UBBERKE ATTORNET.

f receiver.

Patented Mar. 3l, 194,2

Hans Dubberke, Berlin, Germany,

assigner to Telefunken Gesellschaft Eiir Drahtlose Telegraphie m. l. il., Mrlin,

tion of Germany Germany, a corpora- Application January d, 1939, Serial No. 249,238

l Claims.

This invention relates to amplifying apparatus, and will be explained more fully by reference to the'appended drawing, wherein Figure 1 shows an exemplified embodiment of a circuit arrangement in which the steps here disclosed have been adopted, and Figure 2 shows the identical scheme in the form of afbridge arrangement so that the effect and operation V,of the invention may be understood more clearly.

It is known in the prior art according to Fig. l lto tap the grid biasing potential for a tube across a resistance W1 which is traversed by the plate current of all tubes. Inasmuch as in the resistance W1 there still exists an alternating potential originating from the supply-line or mains (ripple), the smoothing means indicated by the dash-lines is connected between the grid leak Rg and resistance W1, or at least resistance `W1 is bridged or shunted by a condenser. Now,

according to the invention, the said smoothing means is rendered dispensable. Especially in small-'sized receiver sets, for instance,- single circuit receivers comprising two tubes, the resultant savingv means so much that the use of the invention is noticeable to an appreciable extent in the reduction of the total cost of the What is essential is that in using the invention, organizations known in the prior art are utilized which require additional circuit elements or in t which smoothing means must be dimensioned to n insure compensation of hum.

'I'he inventionisconcerned with a receiver or amplifier with mains connection which comprises at least .two resistance-coupled tubes with va resistance (W1) included in the joint plate lead at the mains end of the last smoothing con denser-. (Cz) for the negative grid biasing potential oithe second tube which is not to be lterd any more.

According to the invention, the couplingy elements of the resistance amplifier stage (R11, C1, Rg) andthe resistance W1 for the negative grid biasing voltage of the second tube and-the last smoothing condenser (C2) in comparison to the inner resistances of the twotubes (I, II) are so dimensioned that such disturbing alternating potential as may still prevail betweenthe positive pole (-i-A') of the smoothed plate potential for Germany January 19, 193@ (ci. irs-ern) none of the compensation circuit tube II no longer exists.

both tubes and the negative end (-A) of the biasing voltage resistance, and which acts in the bridge arrangement formed by all of the said circuit elements will not allow any essential alternatlng voltage to arise between the grid-filament 'from the D. C. supply line or mains or from a rectiiler in case of an A. C. supply line, is connected across the terminals -A and +A. and it is'smoothed by the aid of the condenser Cs, Cz and resistance W2. Across the resistance W1, as stated, arises the grid biasing potential for the power tube. The screen grid of the power tube 4is united with the positive pole +A' of the smoothed plate potential.

In the bridge arrangement shown in Fig. 2 the same denotations yare used in Fig. 1, with the addition of the values which have been ascertained by test in a particular circuit. The inner resistance of the tube I as well as the inner resistance of the cathode-screen-grid path of tube II were each around 50,000 ohms. The inner resistance of the filament-plate path of power tube II, as will be seen, is so high that it mayA be neglected in comparison with the bridge balance. The various circuit elements are so dimensioned that a disturbing or stray alternating potential existing across -A and +A' will no longer exist acrossG. and`V K.' It will be remembered that an alternating' potential at this particular place ,is very undesirable for the reason that it would be still further amplified by the power tube II. Aldisturbing alternating voltage arising at tube I will no longer manifest itself seeing that the bridge is so balanced'that the alterhating potential between grid and filament of I For this reason, a distinct smoothing means for the plate current of tube I ls'dlspensable. Any rest or trace of alternating potential which may still prevail at the condenser C2, as a result of control of the screen grid of tube II, will permit only a very small plate alternating current to arise, so ',small, indeed, that it is practically inaudible; but if the bridge is properly adjusted it may also be balanced out.'

The dimensions chosenjor the circuit organization Flg. 1 diiers from the scheme known in quen'cy of the coupling element, however, still The lower cut-olf fretained in the bridge, of course, are also decisive for the operation of the invention.

In the case of direct current and universal receivers, as is well known in th-e art, a condenser aC4 is connected between the cathode and the ground according to Fig. 1, in orderl to ground the cathode for RF. The said condenser enters into the bridge scheme in a way as indicated in Fig. 2 when terminal A is united with the grounded pole of the network. Experiments have demonstrated that for dimensions as indicated in the drawing (Figl 2) for the various circuit elements, the said condenser will still further reduce the line hum to a slight extent. To be sure, the effect is not very essential so that the circuit organization is useful also in cases where terminal +A is united with the grounded pole of the mains. In this case, the condenser is connected between points K and +A, Fig. 2.

Where the line-supply potential is less than 200 V, the internal resistance of the tubes will have somewhat different values; however, practical tests have shown that, because the gain is at the same time somewhat lower, the effect and usefulness of the invention will still be adequate.

I claim:

1. In signalling apparatus including a first electronic tube having an anode, a cathode and I a signal grid, means for impressing signal energy between the signal grid and cathode, a pair of terminals adapted to be connected to a source of direct current having an undesired hum component, one of said terminals constituting a positive terminal and the other thereof a negative terminal, an anode lresistor connected between the positive terminal and said anode, a second tube having an anode, a cathode, a signal grid and a screen grid. a coupling condenser connected between the anode of the first tube and the signal grid of the second tube, a utilizing device connected between the anode of the second tube and said positive terminal, means for connecting the screen grid to said positive terminal, a cathode resistor connected between the negative terminal and both of said cathodes whereby anode current from both of said tubes fiows through said cathode resistor, means including at least a part of said cathode resistor and a grid leak resistor in series for connecting the signal grid of said second tube to 'the cathode.thereof whereby said last named signal grid is biased with respect to mon to the first and second arms thereof and a point of the bridge common to the third and the anode to a point of said third arm which is said last named cathode at least in part by current fiowing through said cathode resistor, said cathode resistor also having fiowing therethrough an undesired hum component from said source whereby said hum Vcomponent is impressed upon the cathode of said second tube, and means for impressing a substantially similar hum component derived from said source upon the signal grid electrode of said second tube to thereby substantially neutralize the. effect of the hum component impressed upon the cathode.

2. In amplifying apparatus, a screen grid tube. a four-arm balanced bridge network having a first arm including a cathode resistor, a second arm adjacent said first arm including a grid leak resistor, a third arm opposite the first arm including a coupling condenser in series with a plate resistor, and a fourth arm opposite the second arm including a filter condenser shunted by the cathode-screen-grid path of said screen grid tube, means for connecting a source of energizing voltage between a point of the bridge comcommon to the coupling condenser and the plate resistor therein, means for connecting the cath# ode to a point of the bridge which is common to the first and fourth arms thereof and means for coupling a source of energyto be amplified between the grid and cathode of said driver tube.

3. In amplifying apparatus, a first tube having an anode, a cathode and a grid, a signal inputA circuit for said first tube connected between the grid and cathode thereof, a source of fluctuating current, an output circuit for said first tube including a plate resistor, said source of said fiuctuating current and a cathode resistor in series connected between the anode and cathode thereof, a second tube provided with an anode, a cathode and a grid electrode, means including a coupling condenser for connecting a point of the output circuit of the first tube to said last named grid electrode, means for biasing the grid electrode of said second tube with respect to the cathode thereof comprising a connection between said grid and cathode including in series a grid leak and said cathode resistor, an output circuit for said second tube comprising a utilizing device, said source of fluctuating current and saidcathode resistor all connected in series in the order named between the anode and cathode thereof', a filter condenser connected between the-source end of the utilizing device and the cathode, fluctuations from said source being impressed upon the output circuit of the first tube, the output circuit of the second tube and the input circuit of the second tube, said coupling condenser and plate resistor, said grid leak resistor, said cathode resistor, and said filter condenser lbeing proportioned so .that substantially thefsame fiuctuating component is impressed up on the grid electrode vof said second tube as on the cathode thereof whereby the effect of the fluctuating component is neutralized. Y'

4. In amplifying apparatus, a 'first tube. having an input circuity and an output circuit, said output circuit including anV anode resistance, a source of fiuctuating current'and a cathode resistance in series, whereby inthe operation of Asaid apparatus there exists in said loutput circuit the fiuctuating component of said source, a second tube having a grid circuit including a grid leakA resistor and said cathode resistor in series, a coupling condenser connecting a point of said anode resistor to a point of said grid circuit through which coupling the fluctuating component in said output vcircuit is transferred to said grid circuit, an output' circuit for said second named tube including in series a utiliz'ng device, the source of fluctuating current and the cathode resistor, -said last named tube having impressed upon its grid circuit a fluctuatingcurrent component due to the inclusion of said cathode resistor in said grid circuit, said coupling condenser and grid leak resistor being proportioned in relation to said anode resistance,

Aing an anode, a grid electrode and a cathode means for impressing signal voltage between the grid electrode and cathode of said tube, an outthe cathode resistor and the arm of the bridge which includes the lter condenser, said sourceof direct current being effectively connected across the other two opposite junction points of the bridge whereby substantially equal hum voltages are produced on the signal grid and cathode of thel second tube.

put circuit for said tube comprising an output"4 impedance, a source of direct current, the output of which has an undesired hum component, and a cathode resistor in series and in the order snamed between the anode and cathode of the "tube, a filter condenser connected between the source end of the output impedance and the cathode, a second tube having an anode, a cathode, a signal grid and anauxiliary grid, a coupling condenser connected between 'a point of said output impedance and said signal grid, a signal grid-cathode circuit for said second tube including a grid leak resistor and at least a portion of said cathode resistor in series, an auxiliary grid-cathode circuit for said second tube including said source of direct currentand said cathode resistor in series, and an anode-cathode circuit for said second tube including a load device, said source of direct current and said cathode resistor in series, said cathode resistor, said grid leak resistor, said coupling condenser in series with said output impedances and said lter condenser shunted by the internal screen gridcathode impedance of said second tube constituting four arms of a balanced bridge arrangement wherein the signal grid of the second tube is connected to the junction point of the arm of the bridge constituted by said grid leak resistor and the arm constituted by the coupling condenser in series with the output impedance, and the cathode of the second tube is connected to the junction point of the arm constituted by 6. In amplifying apparatus including a utilizing device and an amplifier tube, said amplier tube being provided with an anode, a cathode and a grid electrode, a four arm balanced bridge circuit, one of the arms thereof including an impedance and a condenser'in series, an arm adjacent said first arm including an impedance element, the other arm adjacent said iirst arm including a condenser shunted by a circuit including the utilizing device and said amplier tube in series, the arm opposite the rst named arm of the bridge including an impedance element, a source of fluctuating direct current potential connected between a point common to said rst named arm and said second named adjacent arm and a point common to said first named adjacent arm and said opposite arm, a driver stage for said tube including an electronic tube having an anode, a cathode and a signal grid, and means including said first named condenser for connecting the anode of said last named tube to the signal gri'd of the first named tube.

7. In the arrangement described in claim 6, means including the impedance element in the arm opposite the 4first named arm for connecting the cathode of said driver tube to one terminal of the source, and means including the impedance element in said first named arm of the bridge for connecting the anode Iof said driver tube to the other terminal of the source.

' HANS DUBBERIE. 

